I recently replaced the head gasket, turbo, rebuilt fuel injectors, new air vacuum pump, and now that it is back on the road I have to be very carefull not to let it overheat. I am burning used oil and diesel mix but 60mph and below it seems ok but get around 70 mph and it heats up rather quickly. Any suggestions would be appreciated. Thanks

Air bubble in the coolant system comes to mind Check your cooling surface, lightly spray water though the rad when it's cold to make sure air can get through
when you say heats up how high does it get? is there an upper limit or will it get as hot as you let it?

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hum.....
1987 300TD 311,000M Stolen. Presumed destroyed

look for a rag in the radiator... very common after a head gasket change.
either way, your radiator is not flowing well, or your head is cracked.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

I have heard that 100 degrees is the magic number for doing damage, so I have the defrost on at 90-95 degrees and it has still hit 100 for a real short time. Hopefully I can drain and flush the coolant system this weekend to get a better starting point.

Sorry I didn't start my response off right, "Thank You" for helping. I got this car for the ability to burn oil and diesel mix, but sure does seem to be a challenge to keep it on the road any more. Again "Thanks" and I will have a chance to get to it this weekend.

Well before going whole hog on that you can try to "Burp" the system and please check the rad for a rag like Vstech says. It's so easy to drop one down in there and forget about it especially if you've had the head off.

also since you had the head off to do Gasket work, did you have the one (I assume the original one that came off) Pressure tested? when the original gasket went the head could still have cracked and still be cracked now if you diddnt have it looked at.

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hum.....
1987 300TD 311,000M Stolen. Presumed destroyed

Is it possible to retain an air bubble indefinitely? i.e., is it possible that only something like an Airlift would get it out?

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Rob

After the car has gotten hot, parked for 1/2 hour and cooled down, is the upper rad still hard to squeeze? Vent the pressure by opening the coolant reservoir drive and repeat. Hard -> cracked head. Look for oil mix in coolant (dip a paper into the reservoir. Oily -> cracked head.

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Cheers!
Scott McPhee

1987 300D

Another symptom I've noticed is weak heating. It's difficult to imagine a source of blockage, but I'm wondering if an air bubble might still explain this. Sorry to hijack the thread, but it seemed related.

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Rob

Sooner or later, any excess air should make its way to the expansion tank.


"Another symptom?" Looks like weak heating is the only symptom you have mentioned. What's the rest of the story?

Ahh, forgive me... Here are the details:

The primary issue is the temperature climbing to 95 degrees on cool days after climbing a hill that's only a half mile long. This, despite replacing the radiator, testing the head, new head gasket, new thermostat, new fan clutch, new G5 coolant, new radiator hoses, testing the temp sensor.

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Rob

There is a good chance that you have a slight pressure leak somewhere. If you haven't pressure tested the system and the cap, that would be a great place to start. Some parts stores will loan a pressure test set. Sometimes it's amazing what a few strokes of the test pump will reveal.

Could very well be an air bubble. The 60x engines seem to be challenged in this regard. Try parking the car on a steep uphill, ramps, etc., and idle the engine with the climate control set to "Defrost." This should force the monovalve wide open and the angle will allow any bubbles to work their way out of the system. If you do not get hot air blasting out of the vents in short order, you could have a blockage in the system, as previously mentioned, a bad monovalve, or a bad auxiliary coolant pump. Any of those could prevent air trapped in the system from escaping.

Since you have been doing a lot of work on the car, here's one more thing you might consider. There are a range of temperature switches for the upper radiator port; this is the three-pin switch that turns on the auxiliary fan as the engine warms up and turns off the air conditioning if it really warms up. You can replace the stock switch (105ºC/128ºC) with one that switches at lower limits, thus helping cool the radiator. My personal choice at the moment is a 100ºC/110ºC switch that you can recognize from the red plastic top.

Part numbers are:
006 545 64 24 (original equipment in OM603 only) 105ºC/128ºC with blue top
006 545 42 24 (used in M102 and OM601 engines) 105ºC/120ºC with gray top
006 545 61 24 (used in M102-3-4 and OM602 engines) 100ºC/110ºC with red top

Don't forget to install the crush washer if you change switches.

Jeremy

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

There's no indication of loss of coolant over time, or of loss of pressure after shutdown, although I haven't performed a pressure test just yet. The recovery tank also looks pristine inside, so I don't think I'm seeing oil in the coolant. I did replace the fan switch with a 105/120 degree version (gray) some time ago. I do wonder about the monovalve or aux pump. Is there a fairly simple way of evaluating those? BTW, I was experiencing this issue before replacing the head gasket, radiator and thermostat.

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Rob

The aux pump draws 0.8 amps at 14 volts, and sounds like it's running. Haven't verified flow yet, though. Might it be non-functional, but running?

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Rob